The invention relates to a dryer for strip- or plate-shaped material, in particular a multilevel dryer for gypsum board or plywood.
WO 84/01424 describes an apparatus for heating or cooling foodstuffs wherein an outer housing holds a blower, nozzle boxes, and a conveyor belt. The blower is so closely juxtaposed upstream of the nozzle that its rotation axis is generally central between the nozzle boxes. The feed chamber between the blower and the intake of the nozzle box is defined by an inner housing. Between the upper and lower nozzle boxes is a hip-roof-shaped guide body. The guide body has engaging well into the feed chamber so that the spacing of this edge from the blower only amounts to about one fourth of the width of the feed chamber. Such a guide body is not suitable for the dryer according to the invention.
Kroll describes in Trockner und Trocknungsverfahren (Springer; 1959; p.75ff) a dryer having a distributor wall with semicircular air-guide bodies that are arranged on the air-entry side of the chambers of a drying chamber. The distributor wall restricts the flow cross section to the chambers, thereby increasing the pressure in the chamber, and leads to a uniform air distribution to the individual chambers. Uniform flow in the individual chambers is not the goal. A chamber dryer is not analogous to this art.
The invention is based on the dryer known from German 197 01 426 where an attempt is made to create uniform drying over the entire material width. This is achieved largely in that the spacing of the nozzles from the surface of the material is adjustable at least at one end of the nozzle box and is different at both ends. It has been shown that drying near the air inlet is less in the nozzle box than over the remaining length of the nozzle box. Tests have shown that in the region immediately downstream of the air inlet in the nozzle box there is turbulence. This is the result of the compact construction of the dryer that allows a relatively high vertically oriented flow speed in the feed chamber upstream of the nozzle boxes. Thus the speed in the air-entry region in the nozzle boxes has, in addition to the horizontal, also a vertical component that creates the turbulence. This means in practice that overall the drying time is increased in order to ensure the maximal permissible residual moisture over the entire material. Thus more energy must be used for drying than would be necessary under optimal circumstances.
It is an object of the invention to provide a dryer with the features of the characterizing clause wherein more uniform drying with better energy use is achieved on the intake side of the nozzle box.
By the use of the invention there is a uniformly directed flow without significant turbulence even in the intake region of the nozzle box. In the nozzle boxes the pressure relationships are largely stable so that the drying air can exit uniformly from all nozzles.
Preferred embodiments of the invention are given.
The drawing serves for describing the invention with reference to simplified illustrated embodiments.